Ecological niche and gradients. Why are there so many species? How is it that so many species can co-exist? Why are some species common and others rare?

Similar presentations

Presentation on theme: "Ecological niche and gradients. Why are there so many species? How is it that so many species can co-exist? Why are some species common and others rare?"— Presentation transcript:

9
Within the range of tolerance there may be further subdivisions Generally better conditions are needed for reproduction than for growth and both of these need better conditions than simple survival. Thus reproduction will limit the actual occurrence of the sp.

10
Niche and gradients The niche defines the total ecological space in which a species could survive. Ecological conditions vary from one place to another, e.g. Warmer, drier, higher pH, salinity, better drained, lack of competitor/predator. Often we can think of these as environmental gradients.

12
Environental factors will affect growth response Generation times may be different through the year. As climate changes growth responses will change.

13
In this example: Temperature is axis 1 Salinity is axis 2 Environmental gradients as axes Organism’s distribution can be defined by its range on an environmental axis

14
With 3 gradients/dimensions Example corals –Respond predictably to light, salinity and temperature. As niche is represented by a cube we can think of it as a volume.

15
What about all the other dimensions? How many dimensions are there….n So we can define a niche as an n-dimensional hypervolume, first introduced by G.E. Hutchinson (1959). This definition is more useful than the “job” definition of niche offered by Elton as it is predictive and can be quantified. The maximum possible range of a species defined in n dimensions is its fundamental niche (i.e. in the absence of competition).

16
With competition the niche space may be reduced Competition prevents occupation of all of fundamental niche. The portion actually occupied in the presence of competition is the realized niche Fundamental niche sp1 Realized niche with 1 competitor

17
With competition the niche space may be reduced Competition prevents occupation of all of fundamental niche. The portion actually occupied in the presence of competition is the realized niche Fundamental niche sp1 And now with 2 competitors

18
Niche and competition Species that compete for the same resource must minimize competition…..15% difference hypothesis for coexistence. Spatial, temporal or physiological separation. Large zone of competition, means resource harder to acquire -> less efficient ->less reproductive success -> lower fitness -> extinction of lineage.

19
Back to ecological gradients We can predict that along an ecological gradient a species will rise to an optimum, decline and be replaced by another species rising to an optimum and so on.

20
One sp. response to a gradient Occurrence of Eragrostis (a sedge) from submerged (left) to high ground (right). Quadrat 2 is at waterline